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6 Twice as Sleepy or Half Alert?

6 Twice as Sleepy or Half Alert?

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of PVT or MSLT findings? Obviously, conceptualising sleepiness in this

manner makes as little sense as would suggesting that hunger can be ‘doubled’ by going without two meals instead of one. Nevertheless, we do use

the language of quantity to describe sleepiness, which is another reason

why language based, subjective scales such as the KSS do have a key role

to play and, in their own way, are just as important and meaningful as

the objective measures.

There are some similar conundrums relating to sleepiness that can be

illustrated by the MSLT. The first is based on the widely acknowledged

average MSLT score being around 12–15 minutes for healthy, good

sleeping adults. It implies that about half the healthy population will fall

asleep faster than this, and suggests that a few minutes or so before falling

asleep they would have been sleepy—sufficiently so to fall asleep. If they

had felt alert prior to entering the MSLT bedroom, then this again shows

that sleepiness can be ‘unmasked’, or maybe even generated in ostensibly

alert people, if they so wish. Of course, it might be argued that this average MSLT latency includes a substantial proportion of the population

with sleep debt, as they fail to attain a potentially desirable much longer

MSLT score, indicative of what might be viewed as ‘full alertness’. But

there is probably little to be gained by asking the participant who has

fallen asleep during the MSLT how sleepy they were prior to dropping

off, as we know that falling asleep itself clouds such a judgement, as will

be seen in the next section.

Another aspect of sleepiness, relating to the normal distribution of

sleep and sleepiness, is as follows. If healthy, fully sleep-satiated people

have their night sleep restricted by a fixed amount, either in absolute or

proportional terms, then due to the normal distribution between people,

some will naturally have shorter MSLT scores than others, despite the

same sleep loss. Alternatively, if the normal sleep lengths for a variety

of healthy sleepers of similar age and sex are ranked so that their MSLT

scores are identical, then presumably there will be a normal distribution

in these sleep durations. A similar finding may well be seen with other

measures of sleepiness despite these constant MSLT scores. These various

normal distributions may well belie more interesting interpretations, not

only in terms of the relationships between sleep durations and MSLT

scores in healthy good sleepers, but have wider implications.



In effect, this all means that for any given ‘quantum of sleepiness’ there

is a normal distribution in the ability of healthy people to fall asleep.

Whilst on the one hand, there will be those people who, naturally, will

need a higher degree of sleepiness before falling asleep, on the other hand,

and excluding those who are actually sleep deprived, there will be some,

in this distribution, who can, if they so wish, fall asleep relatively rapidly but are not necessarily particularly sleepy, as was found in the study

of those patients successfully treated for obstructive sleep apnoea (Sect.

8.2). This ‘high sleepability’, not so much due to sleep loss, is also seen

by us and others [17, 18] in some healthy young adults having very short

MSLT scores, below 6 minutes. To test whether they really were sleepy,

we [16] gave them a much longer PVT session, lasting half an hour. But

there were no lapses and their reaction times were normal—in fact better

than normal. That is, they seemed quite able to decide whether or not to

fall asleep, when in the appropriate circumstances.


Road Safety

With the possible exception of certain severe clinical conditions (e.g. narcolepsy), sleep does not occur spontaneously from an alert state. There

is always a feeling of sleepiness beforehand, and apart from our findings

clearly demonstrating this [19, 20] other research groups have also done

so [21]. Thus, it is not possible to be alert one minute and asleep the

next—certainly if one has no intention of falling asleep. This has important medico-legal implications for drivers who fall asleep at the wheel

[22], who often claim that before the collision they had no feeling of

sleepiness and thus fell asleep without forewarning. However, as we have

seen, when given a few minutes to settle down, people have good insight

into any sleepiness.

Somewhat paradoxically, and apart from sleep itself, sleepiness also

clouds one’s memory for recent sleepiness, as we have also found [17]

when using a real car interactive road driving simulator, where drivers

who had their EEG’s recorded, with their faces monitored for eye closures,

had to report their level of sleepiness (using the KSS) every few minutes

during the drive. Although those having a microsleep at the wheel (seen




in the EEG and by eye closure) are quite able to declare beforehand,

that they feel sleepy, they cannot remember this actual feeling after the

drive, despite remembering saying that they were sleepy. This phenomenon applies to all of us with, for example, our usual failing to remember,

today, the actual feeling of sleepiness and how sleepy we were before bedtime last night and, particularly, when this became noticeable. The same

applies to hunger and thirst—we can seldom remember either in any

detail even a short while after a meal or drink, even though it was clear

at the time that we were hungry or thirsty. The reason is that the human

brain does not have the capacity to remember such pointless information

after the consummatory acts of sleeping, eating and drinking.

Yet, sleepy drivers often reach a point of ‘fighting sleep’ revealed by

their opening the car window (for fresh air), turning up the radio, stretching and so on, which must be self-evident that they are sleepy. Sleep is

a dangerous state, and all living organisms are provided with behaviours

necessary to ensure that they do not fall asleep spontaneously, and have

forewarning to allow them to reach a place of relative safety. But the real

problem, here, is that drivers will often continue to drive in this state,

taking the risk in believing that they are able to remain awake, but are

actually unable to predict if and when they will fall asleep. Of course, if

someone is driving in the small hours of the morning, when they would

usually be asleep in bed, and knowingly have had little sleep that night,

then this is another reason why sleepiness would be self-evident.

In having fallen asleep, and then to know that one has been asleep,

this sleep has to last at least a minute or so. Waking someone up who

has momentarily ‘dropped off’ unexpectedly with an unscheduled sleep

of less than this duration usually results in the sleeper's genuine disbelief

of having been asleep. Sleepiness and the process of falling asleep clouds

one’s ability to know whether one is asleep or awake during this initial

transition period. Which is a reason why most drivers who momentarily

fall asleep for a few seconds at the wheel and have a collision subsequently

have little recollection of actually having fallen asleep.





Sleepiness as a propensity to fall sleep and as an index of the ‘biological need for sleep’ are not necessarily synonymous, as its various measures reflect both essential and less or even non-essential aspects of sleep.

That is, these measurement devices and their varying methodologies also

encompass, to varying extents, different qualitative aspects of sleepiness

apart from its intensity, that depend on, for want of a better term, ‘the

influence of the mind’. Besides, as neither sleep nor sleepiness seem to

reflect uniform, equally proportional or numerically equivalent dimensions, then statistically significant outcomes can sometimes have less biological, psychological or clinical significance, or even obscure real sleep

needs. Furthermore, the more sensitive a test of sleepiness is, especially in

the laboratory environment, then the more it will be able to eke out the

relatively inconsequential aspects of sleep and sleepiness. Thus, levels of

sleepiness ‘unmasked’ in the laboratory by refined tests, but small enough

to be unnoticed by healthy people leading normal lives in more stimulating environments, should make us circumspect in assuming these levels of sleepiness to be realistic, especially when these lead to claims of

chronic ‘sleep debt’ in the general population. It is even possible that

sleepiness can be generated de novo by a particularly dull and tedious

situation. Nevertheless, I have argued that people do have good ‘online’

insight into their own sleepiness, whereas experimental findings indicating otherwise seem largely an artefact of the methodologies. Sleepiness is

potentially life-threatening and for Nature not to have made provision

for us to detect this in ourselves is most unlikely. The real danger for

sleepy people is for them to ‘consciously deny’ their sleepiness and take

sleepiness-related risks.


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Extreme Sleepiness


Badly Disrupted Sleep

Inadequate sleep comes in various forms. For example, it can just be too

short, or at the wrong time of the day as in shift work, where both can

produce excessive daytime sleepiness (EDS). Alternatively, this inadequacy can be more of a subjective state, as we have seen with insomnia,

where the patient’s distress is not so evident in objectively defined sleep

when seen with overnight polysomnography (PSG) and absence of EDS.

During normal sleep we naturally move and change position, momentarily, about five times an hour, which usually necessitate short, 2–3 second, waking arousals. Such interruptions are unnoticeable and too short

to cause any real sleep disturbance. However, when they become longer

and more frequent, then this impaired sleep can become an even greater

factor in determining waking well-being than can sleep duration, with

the key sign usually being EDS, depending on the severity of the disruptions. For a sleeper to realise they have woken up during the night and

to have remembered this next morning, they usually have to be actually

awake for at least 30 seconds, more likely a minute or so, which is why

short duration awakenings due to obstructive sleep apnoea (OSA) and

© The Editor(s) (if applicable) and The Author(s) 2016

J. Horne, Sleeplessness, DOI 10.1007/978-3-319-30572-1_9




periodic limb movement disorders of sleep (PLMD, see below) go unnoticed by the sleeper, despite occurring frequently during sleep. Sufferers

are usually oblivious to their sleep having been so grossly disturbed, and

may well believe that they have slept well. Such persistent daytime sleepiness, day after day, month after month, can reach such a chronic level

that the patient ‘forgets’ what it is like to be normally alert, to the extent

that they may well think this sleepiness is ‘normal’ for them. Treatments

(mentioned below) can be remarkably effective and rapid, often dramatically noticeable to the patient, literally overnight, when they can wake up

feeling sufficiently alert to realise how persistently sleepy they had really


Thus, inadequate sleep has marked contrasts, reflected by insomnia on

the one hand, with its hyperarousal and perceived poor sleep, to OSA and

PLMD, with both the latter usually accompanied by EDS and with the

patient often unaware that their sleep is so poor. These latter two are the

most prevalent sleep disorders in terms of severity of sleep disturbances

and provide other important perspectives on sleep quality and sleepiness, which I will describe. The rarer narcolepsy-cataplexy will provide

yet another perspective.


Excessive Daytime Sleepiness (EDS)

The most commonly used subjective scale for assessing EDS, is the

Epworth Sleepiness Scale [1], which is self-explanatory:

The Epworth Sleepiness Scale (ESS)

How likely are you to doze off or fall asleep in the following situations, in

contrast to just feeling sleepy?

For each of the situations listed below give yourself a score of 0 to 3,


0 = Would never doze

1 = Slight chance

2 = Moderate chance

4 = High chance

Work out your total score by adding up the scores for situations 1–8.


Extreme Sleepiness


If you have not been in one of these situations recently, think about

how you might have been affected.









Sitting and reading

Watching TV

Sitting inactive in a public place (e.g. cinema, theatre, meeting)

As a passenger in a car for an hour without a break

Lying down to rest in the afternoon

Sitting and talking to someone

Sitting quietly after lunch (when you’ve had no alcohol)

In a car while stopped in traffic


Conventionally, EDS is diagnosed when these scores total 11 and



Obstructive Sleep Apnoea (OSA)

OSA is the commonest form of severe sleep disruption, seen and heard by

very heavy snoring. Patients with OSA can have no EDS, with ESS scores

within the normal range, which suggests that the mechanisms underlying

sleep cope with or adapt to this degree of sleep disturbance and, hence,

symptoms are even more likely to go unnoticed by sufferers. This apparently milder OSA is not accompanied by the hyperarousal as happens

with insomnia. However, when OSA reaches the point to cause EDS,

then it is called ‘OSA syndrome’ (OSAS); that is ‘syndrome’, here, is

synonymous with EDS.

The upper airway at the back of the throat is a rather flabby tube

largely kept open by surrounding muscle tension, normally allowing the

free flow of air in and out of the lungs when breathing during wakefulness. In sleep these muscles relax, and during inhalation this part of the

airway, known as the ‘oropharynx’, sags inwards owing to the lower air

pressure, as happens when breathing in. Too much of this ‘flabbiness’

leads to ‘vibrations’, which is, the more normal, mild snoring. Usually, we

breathe through the nose during sleep, with mouth closed, thus clamping

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